Extruding a ferrocyanide containing viscose into a nickel salt containing bath



United States Patent EXTRUDING A FERROCYANIDE CONTAINING VISCOSE INTO A NICKEL SALT CONTAINING BATH Ivan Keith Miller, Bon Air, Va., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Oct. 16, 1957, Ser. No. 690,436

7 Claims. (Cl. 18-54) The present invention relates to a novel and useful process for the production of a shaped structure of regenerated cellulose. More particularly it relates to a process for the production of a shaped structure of regenerated cellulose such as a filament, ribbon, film and the like having improved properties.

It is known that the properties, particularly the strength, of viscose yarns and cords are improved by the reduction of the primary swelling of the gel fibers. The great importance of gel swelling in viscose spinning operations has attained full recognition in recent years and it has become common practice to add certain compounds to the viscose, to the coagulating and regenerating bath, or both to obtain the maximum reduction in the gel swelling of the freshly regenerated filaments. A number of these coagulation modifiers are described in US. Patents 2,535,044, 2,535,045, 2,536,014 and 2,696,423. While the prior art coagulation modifiers are effective in many types of coagulating and regenerating baths, it has been found that when nickel is substituted for the commonly used zinc in the spinning bath, these prior art compounds .are either completely ineffective or have only a slight eifect. In View of the fact that baths containing nickel rare advantageous from many standpoints, as shown by US. 1,596,906, US. 1,899,725 and British 492,418, it

would be highly desirable to find coagulation modifiers which are useful with such baths.

It is an object of this invention therefore to provide a process for producing shaped structures of regenerated cellulose having a low gel swelling. Another object is to provide a process for the production of shaped structures of regenerated cellulose having low gel swelling when spinning into coagulating and regenerating baths containing nickel. Other objects will become apparent hereinafter as the description of the invention proceeds.

These objects are accomplished by the present invention which provides an improvement in the process of pro ducing a shaped structure of regenerated cellulose by extmding viscose into an acid sulfate coagulating and regenerating bath containing at least 1% by weight of a nickel compound, calculated as nickel sulfate, the improvement comprising adding a small amount of a soluble ferrocyanide to the viscose prior to extrusion. The term a soluble ferrocyanide is used to designate a ferrocyanide compound which dissolves in the viscose. Among the various compounds which may be used for this purpose are the alkali metal ferrocyanides, ammonium ferrocyanide, etc.

The invention is illustrated by the following examples which are cited to illustrate the invention but are not intended to limit it in any manner. In these examples the gel swelling of the yarn is determined on small samples (10 grams) of the freshly spun yarn which is collected on a bobbin or feed wheel prior to its entry into the hot secondary bath. The sample is centrifuged at 3600 rpm. for 5 minutes, weighed, washed free of acid and salt, dried in an oven at 105-110 C. and weighed again. The ratio of the first weight (the weight 2,960,335 Patented Nov. 15 1960 ICC EXAMPLES Viscose containing 5.0% recoverable cellulose and 6.5% total alkali, calculated as sodium hydroxide, is prepared in the conventional manner using 60% carbon disulfide. The viscose is filtered, deaerated and ripened to a salt index of 24-26 and a viscosity of 42 poises. The viscose is then extruded into a coagulating and regenerating bath containing 7.8:0.4% sulfuric acid, 5.0:0.2% nickel sulfate and 18.5i0.5% sodium sulfate, the bath being maintained at a temperature of 60 C. The yarn is passed for a distance of 20 inches through the primary coagulating and regenerating bath and then for a further distance of 15 inches through a hot aqueous secondary bath consisting of 2% sulfuric acid and main tained at a temperature of -97" C. The yarn is stretched 110% in the secondary bath. After passing through the secondary bath, the yarn is wound on a bobbin at a speed of 28 y.p.m. The yarn is subsequently ptuified and dried in the conventional manner.

The gel swelling of the yarn is determined as described above on samples of yarn taken just before the yarn passed into the hot secondary bath. Part of the yarn, which has a denier of 1100, is twisted into two-ply cord having a denier of 2450 for testing. The DB fatigue resistance is then determined by conditioning a cord for 48 hours at 24 C. and 54% relative humidity, clamping it in jaws set 16.75 inches apart, and thereafter applying a load of 1 gram per denier to the cord. The temperature of the cord is then raised to C. while in place in the machine for about /2 hour. The jaws are thereafter oscillated to stretch the cord 3,000 times per minute using a stroke of 0.24 inch. The fatigue rating of the cord is expressed in terms of the number of minutes elapsed when the cord fails.

Gel swelling values and other properties are shown in Table I. Also given are the results obtained when the above test is repeated except that sufficient potassium ferrocyanide is added to the viscose during mixing to give the concentrations shown in Table I.

Table I Cord Properties Percent Gel Example K Fe(CN) Swelling Condi- DB Fatigue tioned Resistance, Tenacity, Min.

g.p.d

The ferrocyanide of this invention is preferably added to the viscose in the form of potassium ferrocyanide, K Fe(CN) -3H O, which is readily available but may be added in the form of the sodium, ammonium or any other soluble ferrocyanide. The alkali metal ferrocyanides are preferred. In view of the high concentration of sodium ion in theviscose, the ferrocyanide will presumably be largely converted to the sodium salt regard- 'less of the form in which it is added. The ferrocyanide is conveniently added to the viscose during the mixing operation but may be added to any of the viscose ingredients or mixed in the viscose any time prior to spinning. The concentration of ferrocyanide required to achieve the desired results will vary with the composition of the viscose, the composition of the spinning bath and other factors involved in the process. It is generally desirable that the viscose contain at least 0.1% of the ferrocyanide, calculated as K Fe(CN) and the preferred range is from about 0.25 to about 2.0%. Small amounts will, however, give some reduction in gel swelling and so lesser amounts or other less soluble ferrocyanides may be employed although the results are not as outstanding.

The nickel may be added to the spinning bath in the form of any of its soluble salts such as nickel sulfate, nickel chloride, nickel acetate or nickel nitrate. However, since most spinning baths contain considerable quantities of sulfate and it may be undesirable to add other anions, nickel sulfate is preferably used. The concentration of nickel must be at least 1%, calculated as nickel sulfate, The maximum concentration which should be employed will depend on the solubility of the compound used and many other process variables. In general, the preferred concentration range is from about 3 to about 10%.

I In the process of this invention the viscose solution is prepared in the conventional manner. Alkali cellulose is first prepared by soaking sheets of wood pulp or cotton linters pulp in sodium hydroxide solution. The excess alkali is then drained and pressed from the saturated sheets. The resulting alkali cellulose is shredded and then aged to provide the desired viscosity in the prepared viscose. The shredded alkali cellulose is dropped into a rotatable drum called a barratte where xanthation occurs.

The alkali cellulose may be completely xanthated in the barratte or partially xanthated in the barratte and partially in the mixer. Splitting xanthation so that not over 90% is completed in the barratte is described in U.S.P. 2,801,998 issued to A. Robertson. In either conventional or split xanthation, at least 30% carbon disulfide, based on the cellulose content of the alkali cellulose, should be used. v

The xanthated or partially xan-thated alkali cellulose is now added to a tank where it is mixed with a measured quantity of dilute aqueous sodium hydroxide solution. The amount of sodium hydroxide solution is suflicient to provide a final viscose solution containing 4% to 9% cellulose or more and 4% to 9% or more total alkali calculated as sodium hydroxide. The standard viscoses of the industry, i.e., those having between 5% and 8% cellulose and between 5% and 7% alkali, are preferably used.

The viscose solution is filtered, deaerated and may be permitted to ripen at a temperature of about 18 C. to the desired salt index. While the process of this invention yields improved properties with ripe viscoses it is preferable to restrict ripening and spin the viscose in an unripened or a partially ripened state, i.e., salt indexes of 10 and higher.

The viscose may be extruded hot or cold. Heating may be accomplished by passing the viscose solution through .a heat exchanger using hot oil, hot water, steam, or

heated coagulating bath as the source of heat, or an electric heating unit may be inserted in the pipe.

The spinning bath is preferably maintained at a temperature between about 40 C. and about 80 C. and contains 4% to 10% sulfuric acid, 5% to 25% sodiumsulfate and at least 1.0% of a soluble nickel compound, calculated as nickel sulfate.

The filaments may be extruded through a spinning tube to confine the filaments in the critical stage of formation as described in U.S. Patent 2,440,057 to F. R. Millhiser. After extrusion, the filaments may travel through about 25 to 150 inches in the primary bath where they may be confined to a small area by means of a multiple roller set-up. The rollers are designed to apply tension to the traveling filaments in gradual increments and thereby orient them while they are still plastic. A preferred method is to apply a part of the stretch beyond the primary bath by passing the filaments through a secondary bath or shower located between two power driven rollers. The secondary bath may consist simply of water or of dilute (1% to 4%) sulfuric acid, or it may be diluted spinning bath at a temperature between 50 C. and 100 C. Total stretches of or more are preferred for producing high tenacity yarns and as low as 30% may be acceptable for textile type yarns. From the last roller, the yarn may be wound on a bobbin or fed into a rotating bucket to form a cake and then washed and slashed. The slashing operation is well known and consists of stretching the yarn and applying a lubricating solution.

The shaped structures produced by this invention have outstanding properties and may be used for any purpose where regenerated cellulose shaped structures are presently used. The yarns and cords are useful for reinforcement of rubber articles such as automobile tires and in various textile uses. The ribbons and films are useful as packaging material and the like.

Many other equivalent modifications will be apparent to those skilled in the art from a reading of the foregoing without a departure from the inventive concept.

What is claimed is:

1. In the process of producing a shaped structure of regenerated cellulose by extruding viscose into a sulfuric acid-zinc sulfate coagulating and regenerating bath containing at least 1% by weight of a soluble nickel salt, calculated as nickel sulfate, the improvement which comprises adding a small amount of a soluble ferrocyanide to the viscose prior to extrusion.

2. The process of claim 1 wherein the soluble ferrocyanide is an alkali metal ferrocyanide.

3. The process of claim 1 wherein the soluble ferrocyanide is potassium ferrocyanide.

4. The process of claim 1 wherein the soluble ferrocyanide is sodium ferrocyanide.

5. The process of claim 2 wherein the alkali metal ferrocyam'de is added in amounts of from about 0.25 to about 2.0% by weight.

6. The process of claim 5 wherein the acid sulfate coagulating and regenerating bath is at a temperature of from about 40 C. to about 80 C.

7. The process of claim '6 wherein the alkali metal ferrocyanide is potassium ferrocyanide.

References Cited in the file of this patent UNITED STATES PATENTS 1,899,725 Richter Feb. 28, 1933 2,011,227 Maxwell Aug. 13, 1935 2,114,915 Davis Apr. 19, 1938 2,593,466 MacLaurin Apr. 22, 1952 2,648,611 Richter Aug. 11, 1953 2,705,184 Drisch Mar. 29, 1955 2,732,279 Tachikawa Jan. 24, 1956 FOREIGN PATENTS 848,685 Germany July 3, 1952 

1. IN THE PROCESS OF PRODUCING A SHAPED STRUCTURE OF REGENERATED CELLULOSE BY EXTRUDING VISCOSE INTO A SULFURIC ACID-ZINC SULFATE COAGULATING AND REGENERATING BATH CONTAINING AT LEAST 1% BY WEIGHT OF A SOLUBLE NICKEL SALT, CALCULATED AS NICKEL SULFATE, THE IMPROVEMENT WHICH COMPRISES ADDING A SMALL AMOUNT OF A SOLUBLE FERROCYANIDE TO THE VISCOSE PRIOR TO EXTRUSION. 